Re: [PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
On Fri, Jul 13, 2018 at 11:59:44AM -0700, Andy Lutomirski wrote:
> On Wed, Jul 11, 2018 at 4:29 AM, Joerg Roedel wrote:
> > From: Joerg Roedel
> >
> > Warn the user in case the performance can be significantly
> > improved by switching to a 64-bit kernel.
>
> ...
>
> > +#ifdef CONFIG_X86_32
> > + if (boot_cpu_has(X86_FEATURE_PCID)) {
>
> I'm a bit confused. Wouldn't the setup_clear_cpu_cap() call in
> early_identify_cpu() prevent this from working?
Right you are, I don't have a PCID capable system at hand for testing,
so I didn't catch this...
> Boris, do we have a straightforward way to ask "does the CPU advertise
> this feature in CPUID regardless of whether we have it enabled right
> now"?
I guess we need to call cpuid again.
Regards,
Joerg
Re: [PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
On Fri, Jul 13, 2018 at 11:59:44AM -0700, Andy Lutomirski wrote:
> On Wed, Jul 11, 2018 at 4:29 AM, Joerg Roedel wrote:
> > From: Joerg Roedel
> >
> > Warn the user in case the performance can be significantly
> > improved by switching to a 64-bit kernel.
>
> ...
>
> > +#ifdef CONFIG_X86_32
> > + if (boot_cpu_has(X86_FEATURE_PCID)) {
>
> I'm a bit confused. Wouldn't the setup_clear_cpu_cap() call in
> early_identify_cpu() prevent this from working?
Right you are, I don't have a PCID capable system at hand for testing,
so I didn't catch this...
> Boris, do we have a straightforward way to ask "does the CPU advertise
> this feature in CPUID regardless of whether we have it enabled right
> now"?
I guess we need to call cpuid again.
Regards,
Joerg
Re: [PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
On Wed, Jul 11, 2018 at 4:29 AM, Joerg Roedel wrote:
> From: Joerg Roedel
>
> Warn the user in case the performance can be significantly
> improved by switching to a 64-bit kernel.
...
> +#ifdef CONFIG_X86_32
> + if (boot_cpu_has(X86_FEATURE_PCID)) {
I'm a bit confused. Wouldn't the setup_clear_cpu_cap() call in
early_identify_cpu() prevent this from working?
Boris, do we have a straightforward way to ask "does the CPU advertise
this feature in CPUID regardless of whether we have it enabled right
now"?
--Andy
Re: [PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
On Wed, Jul 11, 2018 at 4:29 AM, Joerg Roedel wrote:
> From: Joerg Roedel
>
> Warn the user in case the performance can be significantly
> improved by switching to a 64-bit kernel.
...
> +#ifdef CONFIG_X86_32
> + if (boot_cpu_has(X86_FEATURE_PCID)) {
I'm a bit confused. Wouldn't the setup_clear_cpu_cap() call in
early_identify_cpu() prevent this from working?
Boris, do we have a straightforward way to ask "does the CPU advertise
this feature in CPUID regardless of whether we have it enabled right
now"?
--Andy
